An asynchronous machine, such as for example an asynchronous motor or an asynchronous generator, has a cage rotor with a plurality of conductor bars, which are arranged lying next to one another on the circumference of the cage rotor and extending in the axial direction. At their longitudinal ends, the conductor bars are connected to one another in an electrically conducting manner respectively by a short-circuiting ring. In the case of asynchronous machines from a certain power class, circumferential speeds that may be around 250 m/s occur at the cage rotor. With these high circumferential speeds, the strength of the cage rotor has to meet particular requirements, it being known to form the cage rotor with a solid type of construction. The cage rotor has a rotor body, which has longitudinal slots which are distributed uniformly over the circumference and in which the conductor bars are placed. The conductor bars are conventionally produced from copper, silver or aluminum alloys, whereas the rotor cage is conventionally produced from steel.
During the operation of the asynchronous machine, the conductor bars in particular are subjected to a centrifugal force, which may be so high that the conductor bars are lifted out of the conductor bar slots. To remedy this, conventionally a positive connection is provided between the conductor bars and the rotor body. This is achieved, for example, by the conductor bars being arranged in the rotor body and produced such that the conductor bars are undercut by the material of the rotor body in the radial direction. Consequently, a positive connection is produced between the conductor bars and the rotor body, but it is subjected to fatigue and/or creep, in particular when the asynchronous machine is undergoing starting-up and running-down operations.
JP 2001 211615 A describes a rotor with a cage, wherein the cage is produced by hot-isostatic pressing of a powder. WO 2005/124973 A1 discloses a method for producing a rotor in which conductive bars are positioned in longitudinal grooves and are subsequently pressure-treated and heat-treated.